Semiconductor device and fabrication method of the semiconductor device

ABSTRACT

A semiconductor device includes: a semiconductor chip; and an Ag fired cap formed so as to cover a source pad electrode formed on the semiconductor chip. The semiconductor chip is disposed on a first substrate electrode, and one end of a Cu wire is bonded onto the Ag fired cap by means of an ultrasonic wave. There is provided a semiconductor device capable of improving a power cycle capability, and a fabrication method of such a semiconductor device.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation application (CA) of PCT Application No.PCT/JP2017/15306, filed on Apr. 14, 2017, which claims priority to JapanPatent Application No. P2016-083634 filed on Apr. 19, 2016 and is basedupon and claims the benefit of priority from prior Japanese PatentApplication No. P2016-083634 filed on Apr. 19, 2016 and PCT ApplicationNo. PCT/JP2017/15306, filed on Apr. 14, 2017, the entire contents ofeach of which are incorporated herein by reference.

FIELD

The embodiments described herein relate to a semiconductor device and afabrication method of such a semiconductor device.

BACKGROUND

With increasing junction temperature Tj of power modules, power cyclecapabilities have been insufficient under conventional technologies(aluminum (Al) wires). Recently, accordingly, in order to prolonglifetime, copper (Cu) wires may be used instead of the Al wires.Alternatively, upper wirings, e.g. lead materials or electrode pillars,may be used instead of the wires.

However, a power of ultrasonic waves becomes extremely larger than thatof the Al wires when bonding the Cu wires onto semiconductor chips, andthereby devices will be broken.

On the other hand, when using the upper wirings, e.g. lead materials orelectrode pillars, Pb-free solder has been used as bonding materials.However, in the case of such Pb-free solder is used, since a meltingpoint becomes up to approximately the junction temperature Tj (=200° C.)in devices, e.g. silicon carbide (SiC), having a thermal resistance of200° C. or more, and a ΔTj-power cycle also becomes large, the powercycle capability (power cycle lifetime) will be decreased.

SUMMARY

The embodiments provide a semiconductor device capable of improving apower cycle capability, and a fabrication method of such a semiconductordevice.

According to one aspect of the embodiments, there is provided asemiconductor device comprising: a semiconductor chip on whichelectrodes are respectively formed on a front surface side and a backsurface side of the semiconductor chip; and a high-thermal-resistantfired layer formed so as to cover at least a part of the electrodeformed on the front surface side of the semiconductor chip.

According to another aspect of the embodiments, there is provided asemiconductor device comprising: an insulating substrate; first to thirdsubstrate electrodes formed on the substrate; a semiconductor chipdisposed on the first substrate electrode, semiconductor chip on whichelectrodes are respectively formed on a front surface side and a backsurface side of the semiconductor chip; a high-thermal-resistant firedlayer formed so as to cover at least apart of the electrode formed onthe front surface side of the semiconductor chip; a first upper wiringconfigured to connect between the fired layer and the second substrateelectrodes; a second upper wiring configured to connect between theelectrode which is not covered with the fired layer at the front surfaceside of the semiconductor chip, and the third substrate electrodes; anda resin formed to seal the first to third substrate electrodes, thesemiconductor chip, and the first and second upper wirings.

According to still another aspect of the embodiments, there is provideda fabrication method of a semiconductor device comprising: forming ahigh-thermal-resistant conductive layer so as to cover an electrodeformed on a semiconductor chip; and firing process of thehigh-thermal-resistant conductive layer.

According to the embodiments, there can be provided the semiconductordevice capable of improving the power cycle capability, and thefabrication method of such a semiconductor device.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic bird's-eye view showing a semiconductor deviceaccording to a comparative example 1.

FIG. 2A is a diagram showing a state before bonding a Cu wire, in aschematic bird's-eye view showing a semiconductor device according to afirst embodiment.

FIG. 2B is a diagram showing a state after bonding the Cu wire, in theschematic bird's-eye view showing the semiconductor device according tothe first embodiment.

FIG. 3 is a schematic cross-sectional structure diagram showing asimulation model of the semiconductor device according to the firstembodiment.

FIG. 4 is a graphic chart showing an effect of the simulation modelshown in FIG. 3.

FIG. 5 is a schematic bird's-eye view showing a semiconductor deviceaccording to a comparative example 2.

FIG. 6 is a schematic bird's-eye view showing a semiconductor deviceaccording to a second embodiment.

FIG. 7 is a schematic cross-sectional structure diagram showing asimulation model 1 (cap structure) of the semiconductor device accordingto the second embodiment.

FIG. 8 is a schematic cross-sectional structure diagram showing asimulation model 2 (solder structure) of the semiconductor deviceaccording to the comparative example 2.

FIG. 9 is a graphic chart showing a comparison result between thesimulation model 1 and the simulation model 2.

FIG. 10 shows a graphic chart showing a relationship between a ΔTj-powercycle and a power cycle lifetime.

FIG. 11 is a diagram showing a state where a wire material is cracked.

FIG. 12 shows a graphic chart showing a state where an amount of strains(distortions) is saturated with lapse of time.

FIG. 13A is a diagram showing a semiconductor chip, in a diagram showinga fabrication method of the semiconductor device according to the firstor second embodiment.

FIG. 13B is a diagram showing a mask printing process, in the diagramshowing the fabrication method of the semiconductor device according tothe first or second embodiment.

FIG. 13C is a diagram showing a drying process, in the diagram showingthe fabrication method of the semiconductor device according to thefirst or second embodiment.

FIG. 13D is a diagram showing a firing process, in the diagram showingthe fabrication method of the semiconductor device according to thefirst or second embodiment.

FIG. 14 is a photograph of a silver (Ag) fired cap fabricated by thefabrication method shown in FIG. 13.

FIG. 15A is a bird's-eye view diagram, which is a configuration diagram(photograph) a module formed by using the semiconductor device accordingto the second embodiment.

FIG. 15B is a top view diagram, which is a configuration diagram(photograph) a module formed by using the semiconductor device accordingto the second embodiment.

FIG. 16 is a configuration diagram (photograph) after molding the moduleshown in FIG. 15.

FIG. 17 shows a photograph to which the module shown in FIG. 15 ispartially enlarged.

FIG. 18 shows a photograph to which the module shown in FIG. 15 ispartially enlarged.

FIG. 19 shows a photograph showing the whole module shown in FIG. 15.

FIG. 20 shows a photograph to which the module shown in FIG. 15 ispartially enlarged.

FIG. 21 is a schematic configuration diagram of a module formed by usingthe semiconductor device according to the first embodiment.

FIG. 22 is a schematic diagram of change of an electric current and atemperature, in a ΔTj-power cycle test of the semiconductor deviceaccording, to the first or second embodiment.

FIG. 23 shows an example of a temperature profile in a thermal cycletest of the semiconductor device according to the first or secondembodiment.

FIG. 24A is a schematic circuit representative diagram of the SiC MISFETof a 1-in-1 module, which is the semiconductor device according to thefirst or second embodiment.

FIG. 24B is a schematic circuit representative diagram of an InsulatedGate Bipolar Transistor (IGBT) of the 1-in-1 module, in thesemiconductor device according to the first or second embodiment.

FIG. 25 is a detail circuit representative diagram of the SiC MISFET ofthe 1-in-1 module, which is the semiconductor device according to thefirst or second embodiment.

FIG. 26A is a schematic circuit representative diagram of the SiC MISFETof the 2-in-1 module, which is the semiconductor device according to thefirst or second embodiment.

FIG. 26B is a schematic circuit representative diagram of the IGBT ofthe 2-in-1 module, which is the semiconductor device according to thefirst or second embodiment.

FIG. 27A is a schematic cross-sectional structure diagram of the SiCMISFET, which is an example of a semiconductor chip to be applied to thesemiconductor device according to the first or second embodiment.

FIG. 27B is a schematic cross-sectional structure diagram of the IGBT,which is an example of a semiconductor chip to be applied to thesemiconductor device according to the first or second embodiment.

FIG. 28 is a schematic cross-sectional structure diagram showing an SiCMISFET including a source pad electrode SP and a gate pad electrode GP,which is an example of the semiconductor chip to be applied to thesemiconductor device according to the first or second embodiment.

FIG. 29 is a schematic cross-sectional structure diagram of the IGBTincluding an emitter pad electrode EP and a gate pad electrode GP, whichis an example of the semiconductor chip to be applied to thesemiconductor device according to the first or second embodiment.

FIG. 30 is a schematic cross-sectional structure diagram of an SiCDouble Implanted MISFET (SiC DIMISFET), which is an example of asemiconductor chip which can be applied to the semiconductor deviceaccording to the first or second embodiment.

FIG. 31 is a schematic cross-sectional structure diagram of an SiCTrench MISFET (SiC TMISFET), which is an example of a semiconductor chipwhich can be applied to the semiconductor device according to the firstor second embodiment.

FIG. 32A shows an example of a circuit configuration in which the SiCMISFET is applied as a semiconductor chip, and a snubber capacitor isconnected between a power terminal PL and an earth terminal (groundterminal) NL, in a schematic circuit configuration of a three-phasealternating current (AC) inverter composed using the semiconductordevice according to the first or second embodiment.

FIG. 32B shows an example of a circuit configuration in which the IGBTis applied as a semiconductor chip, and the snubber capacitor isconnected between the power terminal PL and the earth terminal (groundterminal) NL, in the schematic circuit configuration of a three-phase ACinverter composed using the semiconductor device according to the firstor second embodiment.

FIG. 33 is a schematic circuit configuration diagram of a three-phase ACinverter composed using the semiconductor device according to the firstor second embodiment to which the SiC MISFET is applied as asemiconductor chip.

FIG. 34 is a schematic circuit configuration diagram of a three-phase ACinverter composed using the semiconductor device according to the firstor second embodiment to which the IGBT is applied as a semiconductorchip.

DESCRIPTION OF EMBODIMENTS

Next, the embodiments will be described with reference to drawings. Inthe description of the following drawings, the identical or similarreference sign is attached to the identical or similar part. However, itshould be noted that the drawings are schematic and therefore therelation between thickness and the plane size and the ratio of thethickness differs from an actual thing. Therefore, detailed thicknessand size should be determined in consideration of the followingexplanation. Of course, the part from which the relation and ratio of amutual size differ also in mutually drawings is included.

Moreover, the embodiments shown hereinafter exemplify the apparatus andmethod for materializing the technical idea; and the embodiments do notspecify the material, shape, structure, placement, etc. of eachcomponent part as the following. The embodiments may be changed withoutdeparting from the spirit or scope of claims.

Comparative Example 1

As already explained, with increasing junction temperature Tj of powermodules, power cycle capabilities have been insufficient under the Alwires. Accordingly, in a semiconductor device according to a comparativeexample 1, as shown in FIG. 1, a first substrate electrode 10B and asecond substrate electrode 20B are connected to each other by means of aCu wire 18. More specifically a semiconductor chip 12 is disposed on thefirst substrate electrode 10B, an ultrasonic wave is applied to apredetermined position 18B of a source pad electrode 14 on thesemiconductor chip 12, and thereby the Cu wire 18 is bonded thereto.Reference sign 16 denotes a gate pad electrode.

According to the semiconductor device according to the comparativeexample 1, however, when bonding the Cu wire 18 thereto, since anextremely large power of the ultrasonic wave is required, the devicewill be broken. Alternatively, since it is necessary to make a structureof a pad in order to prevent such a break, the device structure becomescomplicated.

First Embodiment (Semiconductor Device)

FIG. 2 is a schematic bird's-eye view of a semiconductor deviceaccording to a first embodiment.

As shown in FIG. 2A, the semiconductor device according to the firstembodiment includes: a semiconductor chip 12; and ahigh-thermal-resistant fired layer 22 formed so as to cover a source padelectrode 14 formed on the semiconductor chip 12.

For example, a silver (Ag) fired layer or copper (Cu) fired layer may beused as the high-thermal-resistant fired layer 22. Hereinafter, the Agfired layer is called “Ag fired cap 22”, and the Cu fired layer iscalled “Cu fired cap 22.”

As shown in FIG. 2B, the semiconductor chip 12 is disposed on a firstsubstrate electrode 10B, and one end of a copper wire 18 is bonded ontothe Ag fired cap 22 by means of an ultrasonic wave. Moreover, anotherend of the copper wire 18 is bonded to a second substrate electrode 20Bby means of the ultrasonic wave.

Alternatively, an Al wire or clad wire may be applied thereto instead ofthe copper wire 18. A center portion of the clad wire is formed byincluding Cu, and Al is bonded so as to cover the Cu at the centerportion. The clad wire has a high thermal resistance and low thermalresistivity compared with the Al wire.

In this case, the first substrate electrode 10B and the second substrateelectrode 20B can also be composed by a conduction pattern of a chipmounting surface side of an insulating substrates (circuit substrate),e.g. circuit substrates (e.g., a Direct Bonding Copper (DBC) substrate,a Direct Brazed Aluminum (DBA) substrate or an Active Metal Brazed(Active Metal Bond) (AMB) substrate) composed by including a contactedbody of metal/ceramics/metal. As metallic materials of thefront-surface-side electrode and back-surface-side electrode of theinsulating substrate, the same material (s) is fundamentally used. Forexample, a Cu/Al₂O₃/Cu structure etc. are applicable to the DBCsubstrate, an Al/AlN/Al structure etc. are applicable to the DBAsubstrate, and a Cu/Si₃N₄/Cu structure etc. are applicable to the AMBsubstrate. However, a function of the front-surface-side electrode and afunction of the back-surface-side electrode are slightly different fromeach other. The front-surface-side electrode has a function of bondingchips, electrodes, etc., a function as a positive (P) side powerelectrode, a negative (N) side power electrode and an output (Out) sidepower electrode respectively formed by cutting the pattern thereof, etc.The back-surface-side electrode has a function of conducting heat belowby being bonded to a cooling apparatus or bonded to a heat spreader.

As mentioned above, the semiconductor device according to the firstembodiment adopts the structure of capping the high-thermal-resistantfiring material (Ag fired body or Cu fired body) on the source padelectrode 14 formed on the semiconductor chip 12. Thereby, since thepower of the ultrasonic wave to be applied thereto when bonding thecopper wire can be buffered, and a break of the device due to a largeloading weight to be applied thereto when bonding the copper wire can beprevented, it becomes possible to improve the power cycle capability.

(Effect of Ag Fired Cap on Reduction of Damage to Device)

FIG. 3 is a schematic cross-sectional structure diagram showing asimulation model of the semiconductor device according to the firstembodiment. In this case, as shown in FIG. 3, an oxide film 25 is formedon the silicon carbide (SiC) based semiconductor chip 12, an aluminum(Al) electrode 26 is formed on the oxide film 25, a gold (Au) thin film28 is formed on the aluminum electrode 26 by means of a plating process,and an Ag fired cap 22 is formed on the Au thin film 28.

In this case, although the aluminum electrode 26 is illustrated, thematerials of the electrode are not limited to aluminum and copper (Cu)may be used therefor.

Moreover, the Au, thin film 28 (thin film for coating electrode surface)is used in order that the Ag fired cap 22 adheres thereto. Instead ofthe Au thin film 28, an Ag thin film or palladium (Pd) thin film may beformed thereon.

FIG. 4 shows a graphic chart showing an effect of the simulation modelshown in FIG. 3. The horizontal axis indicates a layer thickness t ofthe Ag fired cap 22. The vertical axis indicates a maximum principalstress ratio to be applied to the oxide film 25 when applying adisplacement DA to the Ag fired cap 22. In this case, the stress to beapplied to the oxide film 25 when there is no Ag fired cap 22 is set to“1” (Refer to the point P1).

As proved by observing the arrow P shown in FIG. 4, the stress to beapplied to the oxide film 25 can be dramatically reduced when there isthe Ag fired cap 22. More specifically, when the layer thickness t ofthe Ag fired cap 22 is 5 μm, the maximum principal stress ratio isapproximately 0.4 (Refer to the point P2). When the layer thickness t ofthe Ag fired cap 22 is 10 μm, the maximum principal stress ratio isapproximately 0.2 (Refer to the point P3). When the layer thickness t ofthe Ag fired cap 22 is 30 μm, the maximum principal stress ratio isapproximately 0.1 (Refer to the point P4). Although the layer thicknesst of the Ag fired cap 22 is not limited in particular, it is preferableto be approximately 10 μm to approximately 100 μm, for example (Refer tothe line Q).

As mentioned above, the semiconductor device according to the firstembodiment is configured to cap with the Ag fired body the electrodeformed on the device. Since this cap structure realize the function ofthe buffer material, the damage from the copper wire 18 can be reduced.Naturally, using the copper wire 18 achieves extremely strong bonding,and it can produce an effect of increasing the power cycle capability.

Comparative Example 2

As already explained, with increasing junction temperature Tj of powermodules, power cycle capabilities have been insufficient under thealuminum wires. Accordingly, in a semiconductor device according to acomparative example 2, as shown in FIG. 5, the first substrate electrode10B and the second substrate electrode 20B are connected using an upperwiring 24, e.g. a lead material or electrode pillar.

Thus, when using such an upper wiring, e.g. a lead material or electrodepillar, Pb-free solder 17A and 17B is used as bonding materials. ThePb-free solder 17A and 17B is Sn-based solder in which silver (Ag),copper (Cu), tin (Sn), etc. are blended as an additional component,including tin (Sn) as a principal component. However, in the case ofsuch Pb-free solder 17A and 17B is used, since a melting point becomesup to approximately the junction temperature Tj (=200° C.) in devices,e.g. silicon carbide (SiC), having a thermal resistance of 200° C. ormore, and a ΔTj-power cycle also becomes large, the power cyclecapability will be decreased.

Second Embodiment (Semiconductor Device)

FIG. 6 is a schematic bird's-eye view of a semiconductor deviceaccording to a second embodiment.

As shown in FIG. 6, the semiconductor device according to the secondembodiment includes: a semiconductor chip 12; and ahigh-thermal-resistant fired layer 22 formed so as to cover a source padelectrode 14 formed on the semiconductor chip 12, in the same manner asthe first embodiment.

The high-thermal-resistant fired layer 22 is the Ag fired cap 22 (or Cufired cap 22), in the same manner as the first embodiment. Although thelayer thickness t of the Ag fired cap is not limited in particular, itis preferable to be approximately 10 μm to approximately 100 μm, forexample.

The semiconductor chip 12 is disposed on a first substrate electrode10B, and one end of a plate-like upper wiring 24 is bonded on thehigh-thermal-resistant fired layer 22 by means of solder 26A as abonding material. Moreover, another end of the upper wiring 24 is bondedto a second substrate electrode 20B by means of solder 26B as a bondingmaterial. Pb-free solder can be used for the solder 26A, 26B, in thesame manner as the comparative example 2.

As mentioned above, the semiconductor device according to the secondembodiment adopts the structure of capping the high-thermal-resistantfiring material (Ag fired body or Cu fired body) on the source padelectrode 14 formed on the semiconductor chip 12 and of using theconventional solder thereon. Thereby the cumulative equivalent strain(distortion) to be applied to the solder can be reduced, and the powercycle capability can be improved.

(Comparison of Cumulative Equivalent Strain Between Presence and Absenceof Ag Fired Cap)

FIG. 7 is a schematic cross-sectional structure diagram showing asimulation model 1 (cap structure) of the semiconductor device accordingto the second embodiment. As shown in FIG. 7, in the simulation model 1,the Pb-free solder 17A is formed on the Ag fired cap 22. The layerthickness of the solder 17A and 17B is assumed to be 100 μm, and thelayer thickness of the Ag fired cap 22 is assumed to be 50 μm. A backside surface of the substrate electrode 10B is assumed to be cooled at65° C.

FIG. 8 is the schematic cross-sectional structure diagram showing asimulation model 2 (solder structure) of the semiconductor deviceaccording to the comparative example 2. As shown in FIG. 8, in thesimulation model 2, only the Pb-free solder 17A and 17B is used. Morespecifically, the Ag fired cap 22 is not formed on the semiconductorchip 12, but is formed only under the semiconductor chip 12. The layerthickness of the solder 17A and 17B is assumed to be 150 μm.

FIG. 9 is a graphic chart showing a comparison result between thesimulation model 1 and the simulation model 2. The vertical axisindicates a cumulative equivalent strain to be applied to the solder,and the horizontal axis indicates a junction temperature Tj. Thecumulative equivalent strain is used as a measure at the time ofestimating a lifetime of materials, e.g. solder. In the same material,the lifetime becomes shorter as the cumulative equivalent strain becomeslarger.

The line segment S which connects between the point S1 and the point S2shows a change of a cumulative equivalent strain in the simulation model2 (solder structure). As proved from the line segment S, the cumulativeequivalent strain becomes larger as the junction temperature Tj isincreased, in the solder structure.

On the other hand, the line segment C+S which connects between the pointC1 and the point C2 shows a change of a cumulative equivalent strain inthe simulation model 1 (cap structure). As proved from the line segmentC+S, the cumulative equivalent strain is hardly changed due to thebuffering effects of Ag fired cap 22, even if the junction temperatureTj is changed, in the cap structure.

More specifically, according to the cap structure, it is proved that thecumulative equivalent strain can be reduced by approximately 32% whenthe junction temperature Tj is 120° C., compared with the solderstructure (Refer to the points C1 and Si). Moreover, it is proved thatthe cumulative equivalent strain can be reduced by approximately 44%when the junction temperature Tj is 200° C. (Refer to the points C2 andS2).

As mentioned above, according to the cap structure, there is the effectof improving the power cycle capability, or there is the effect ofmaintaining the power cycle capability even if the ΔTj-power cycle,MaxTj, becomes larger.

As expressed in the following equation, the ΔTj-power cycle correspondsto a difference between the maximum MaxTj of the junction temperature Tjwhen the power cycle is turned ON and the junction temperature MinTjwhen the power cycle is turned OFF. The ΔTj-power cycle becomes 100° C.when MaxTj is 150° C. and the MinTj is 50° C., and the ΔTj-power cyclebecomes 150° C. when MaxTj is 200° C. and MinTj is 50° C.

ΔTj=MaxTj−MinTj  [Equation 1]

A relationship between the ΔTj-power cycle and the power cycle lifetimeis expressed, as schematically shown in FIG. 10. Normally, as shown inFIG. 10, the tendency for the lifetime to become longer is observed ifthe ΔTj-power cycle is lower (Refer to T1), and a tendency for thelifetime to become shorter is observed if the ΔTj-power cycle is higher(Refer to T2). Moreover, there is a tendency that: the wire material tobe bonded at a bonding point is easily cracked (Refer to the cracks 18Cshown in FIG. 11); but the wire material bonded at a bonding surface hasa longer lifetime.

(Relationship Between Lifetime of Solder and Cumulative EquivalentStrain)

Subsequently, a calculating method of the fatigue life will now beexplained. A case where a large load which creates an inelasticdistortion (plastic strain, creep distortion) is repeatedly appliedthereto and thereby the fatigue breakdown is caused by the smallrepetition number (equal to or less than 10⁵ cycles) is called a lowcycle fatigue.

A fatigue life of the low cycle fatigue is expressed by theManson-Coffin law shown as follows:

Δε_(p) ·Nj ^(n) =C  [Equation 2]

In Equation 2, Δε_(p) is an amplitude of plastic strain [−], N_(j) is aplastic fatigue (fatigue life) [the number of times], and C and N arerespectively material physical property values.

$\begin{matrix}{{\Delta ɛ}_{ne} = \frac{{ɛ_{a\; c\; \_ \; {ne}}({fin\_ step})} - {ɛ_{a\; c\; \_ \; {ne}}({ref\_ step})}}{2}} & \lbrack {{Equation}\mspace{14mu} 3} \rbrack\end{matrix}$

In Equation 3, ε_(ac_ne) (fin_step) is the cumulative equivalent strainat a second cycle, and ϵ_(ac_ne) (ref_step) is the cumulative equivalentstrain at a first cycle. Since an amount of the strains (distortions) issaturated with the lapse of time as shown in FIG. 12, an intermediatevalue between the first cycle and the second cycle is calculated inEquation 3. According to the Manson-Coffin law, the lifetime isprolonged as Δε_(p) becomes smaller. It is proved that the lifetime ofthe solder is prolonged since the cumulative equivalent strain becomessmaller according to the cap structure.

As mentioned above, the semiconductor device according to the secondembodiment is configured to use the Pb-free solder 17A and 17B on the Agfired cap 22. Accordingly, the stress which solder directly receives isbuffered by the Ag fired cap 22, it becomes possible to reduce thecumulative equivalent strain to be applied to the solder, and to improvethe power cycle capability.

[Fabrication Method]

Hereinafter, a fabrication method of the semiconductor device accordingto the first or second embodiment will now be explained.

Firstly, as shown in FIG. 13A, an Au thin film 28 is formed on an upperportion of the semiconductor chip 12. Subsequently, as shown in FIG.13B, a firing paste 22P is pushed into an opening of a mask 28M using asqueegee 30, and mask printing is applied to an area corresponding tothe source pad electrode 14. Subsequently, as shown in FIG. 13C, thesemiconductor chip 12 on which the mask printing of the firing paste 22P(high-thermal-resistant conductive layer) is already performed is driedon a hot plate 32. Finally, as shown in FIG. 13D, the semiconductor chip12 is annealed (heated and pressurized) by means of heating plates 34Uand 34D. Thus, as shown in FIG. 14, the Ag fired cap 22 can be formed onthe upper portion of the semiconductor chip 12.

Alternatively, a dispensing method may be applied to the above-mentionedprocess, instead of the mask printing. Even if using the dispensingmethod, the fired layer with quality of the same degree can be made.

[Modules]

Hereinafter, configurations of power modules including a plurality ofthe semiconductor devices according to the first or second embodimentwill now be explained.

FIG. 15A is a bird's-eye view configuration diagram (photograph) of amodule using the semiconductor device according to the secondembodiment, and FIG. 15B is a top view diagram thereof. As shown in FIG.15, the first substrate electrode 10B and the second substrate electrode20B are connected to each other with the upper wiring 24. Signalelectrode terminals G1, D1, and S1 and signal electrode terminals G4,D4, and S4 are respectively extracted to the outside from the firstsubstrate electrode 10B and the second substrate electrode 20B.Naturally, it is also possible to connect the substrate electrodes otherthan the first substrate electrode 10B and second substrate electrode20B, with the upper wiring 24. Moreover, a power terminal Pcorresponding to a drain D1 of an MISFET Q1 at a high level side isconnected to the substrate electrode 10B, and a power terminal O (outputterminal) corresponding to a drain D4 of an MISFET Q4 at a low levelside or a source S1 of the MISFET Q1 at the high level side is connectedto the substrate electrode 20B. Furthermore, a power terminal Ncorresponding to a source S4 of the MISFET Q4 at the low level side isconnected to a land electrode connected to the source pad electrode S1of the MISFET Q1 at the low level side through the upper wiring 24. Inthe above explanation, the MISFET Q1 at the high level side and theMISFET Q4 at the low level side correspond to a semiconductor devicewhich is configured to a circuit of a 2-in-1 module as shown in FIG.26A, for example. Alternatively, it may correspond to IGBTs (Q1, Q4) ofa 2-in-1 module as shown in FIG. 26B. The same applies hereafter.

FIG. 16 is a configuration diagram (photograph) after molding the moduleshown in FIG. 15. As shown in FIG. 16, the first substrate electrode 10Band the second substrate electrode 20B are molded with a resin M etc.

FIGS. 17 and 18 show photographs to which the module shown in FIG. 15 ispartially enlarged. As shown in FIGS. 17 and 18, the semiconductor chip12 is disposed on the first substrate electrode 10B. The Ag fired cap 22is formed on the semiconductor chip 12, and the upper wiring 24 isbonded to the Ag fired cap 22 by means of the solder 26A and 26B.

FIG. 19 shows a photograph showing the whole module shown in FIG. 15.FIG. 20 shows a photograph to which the module shown in FIG. 15 ispartially enlarged. As shown in FIGS. 19 and 20, the semiconductor chip12 is connected to the signal electrode terminals G1, D1, and S1 and thesignal electrode terminals G4, D4, and S4 through wires W.

FIG. 21 is a schematic configuration diagram of a module formed by usingthe semiconductor device according to the first embodiment. As shown inFIG. 21, it is also possible to bond a plurality of copper wires 18 toone semiconductor chip 12.

[Bonding Energy]

Subsequently, bonding energy at the time of ultrasonically bonding willnow be explained.

The bonding energy is calculated by integrating a coefficient offriction p, a velocity v, and a pressure P at the time of bonding, witha time period, as shown in the following equation. The coefficient offriction p and the velocity v are functions of the pressure P.Generally, the bonding strength also becomes higher as the bondingenergy becomes higher.

Bonding Energy=∫μ(P)v(P)PdμdvdP  [Equation 4]

[ΔTj-Power Cycle Test]

FIG. 22 shows a schematic diagram of a change of an electric currentI_(C) and a temperature T in a ΔTj-power cycle test of the semiconductordevice according to the first or second embodiment.

As shown in FIG. 22, the ΔTj-power cycle test is a test to which ajunction temperature is relatively risen and dropped at a short-timeperiod, for example, and thereby a lifetime of a wire bonded portionetc. can be evaluated.

The power cycle test repeats electrical connection (ON) anddisconnection (OFF) of the semiconductor device module so that the chipis heated, as shown in FIG. 22. The ΔTj-power cycle test of thesemiconductor device according to the first or second embodiment repeatsthe electrical connection (ON) (the junction temperature Tj=150° C. for2 seconds) and the electrical disconnection (OFF) (time period until itreaches cooling temperature (e.g., junction temperature Tj=50° C., andelectrical disconnection (OFF) time=18 seconds)), for example.

[Thermal Cycle Test]

FIG. 23 shows an example of a temperature profile in a thermal cycletest, in the semiconductor device according to the first or secondembodiment. The thermal cycle test is conducted in the atmospheric air,and is implemented under a range from minus 40° C. to plus 150° C. Theperiod of 1 cycle of the thermal cycle is 80 minutes, and the breakdownis as follows: 30 minutes at −40° C.; 10 minutes (heating time) from−40° C. to +150° C.; 30 minutes at +150° C.; and 10 minutes (coolingtime) from +150° C. to −40° C. No characteristic degradation isobserved, as a result of measuring forward voltage drop Vf and reversebreakdown voltage Vr for every 100 cycles.

Normally, also in the thermal cycle test or the power cycle test, ifdegradation of the bonded portion starts, a resistance is increased andthe forward voltage Vf is also changed in the test of flowing a highforward electric current etc. Even if degradation includingcharacteristic degradation occurs, it can be estimated that the powercycle capability is high if progress of the degradation is slow.

As a result of the above-mentioned ΔTj-power cycle test and the thermalcycle test, the bonding strength of the copper wire 18 or the upperwiring 24 of the semiconductor device according to the first or secondembodiment is sufficiently secured.

Although the first or second embodiment is configured so that the copperwire 18 or the solder 26A is disposed on the Ag fired cap 22 in, it isnot limited to this configuration. For example, it may be configured tobond the upper wiring 24 onto the Ag fired cap 22 by means of Ag firing.The layer thickness thereof can be increased by Ag-firing on the Agfired cap 22. Thus, higher heat resistance can be effectively realizedmore than the case of using the solder 26A, and thereby the reliabilitycan be improved.

[Concrete Examples of Semiconductor Device]

FIG. 24A shows a schematic circuit representative of an SiC MISFET ofthe 1-in-1 module, which is the semiconductor device 20 according to thefirst or second embodiment. FIG. 24B shows a schematic circuitrepresentation of the IGBT of the 1-in-1 module.

A diode DI connected in reversely parallel to the MISFET Q is shown inFIG. 24A. A main electrode of the MISFET Q is expressed with a drainterminal DT and a source terminal ST. Similarly, a diode DI connected inreversely parallel to the IGBT Q is shown in FIG. 24B. A main electrodeof the IGBT Q is expressed with a collector terminal CT and an emitterterminal ET. As the diode DI, a fast recovery diode (FRD) or a Schottkybarrier diode (SBD) may be externally installed. Only a diode formed inthe semiconductor substrate of the MISFET may be used.

Moreover, FIG. 25 shows a detailed circuit representative of the SiCMISFET of the 1-in-1 module, which is the semiconductor device 20according to the first or second embodiment.

Moreover, a plurality of the MISFET may be included in one module. As anexample, five chips (MISFET×5) can be mounted thereon, and a maximum offive pieces of the MISFETs Q respectively can be connected to oneanother in parallel. Note that it is also possible to mount a part offive pieces of the chips for the diode DI thereon.

More particularly, as shown in FIG. 25, a sense MISFET Qs is connectedto the MISFETQ in parallel. The sense MISFET Qs is formed as aminiaturized transistor in the same chip as the MISFET Q. In FIG. 25,reference sign SS denotes a source sense terminal, reference sign CSdenotes a current sense terminal, and reference sign G denotes a gatesignal terminal. Note that, also in the semiconductor chip Q accordingto the first or second embodiment, the sense MISFET Qs is formed as aminuteness transistor in the same chip.

Moreover, FIG. 26A shows a schematic circuit representative of the SiCMISFET of the 2-in-1 module, which is the semiconductor device 20Taccording to the first or second embodiment.

As shown in FIG. 26A, two MISFETs Q1, Q4, and diodes D1, D4 connected inreversely parallel to the MISFETs Q1, Q4 are built in one module.Reference sign G1 denotes a gate signal terminal of the MISFET Q1, andreference sign S1 denotes a source terminal of the MISFET Q1. Referencesign G4 denotes a gate signal terminal of the MISFET Q4, and referencesign S4 denotes a source terminal of the MISFET Q4. Reference sign Pdenotes a positive side power input terminal, reference sign N denotes anegative side power input terminal, and reference sign O denotes anoutput terminal.

Moreover, FIG. 26B shows a schematic circuit representative of the IGBTof the 2-in-1 module, which is the semiconductor device 20T according tothe first or second embodiment. As shown in FIG. 26B, two IGBTs Q1, Q4,and diodes D1, D4 connected in reversely parallel to the IGBTs Q1, Q4are built in one module. Reference sign G1 denotes a gate signalterminal of the IGBT Q1, and reference sign E1 denotes an emitterterminal of the IGBT Q1. Reference sign G4 denotes a gate signalterminal of the IGBT Q4, and reference sign E4 denotes an emitterterminal of the IGBT Q4. Reference sign P denotes a positive side powerinput terminal, reference sign N denotes a negative side power inputterminal, and reference sign O denotes an output terminal.

(Configuration Examples of Semiconductor Chips)

FIG. 27A shows a schematic cross-sectional structure of an SiC MISFET,which is an example of a semiconductor chip which can be applied to thefirst or second embodiment, and FIG. 27B shows a schematiccross-sectional structure of the IGBT.

As shown in FIG. 27A, a schematic cross-sectional structure of the SiCMISFET as an example of the semiconductor chip 110 (Q) which can beapplied to the first or second embodiment includes: a semiconductorsubstrate 126 composed by including an n− type high resistivity layer; ap body region 128 formed on a front surface side of the semiconductorsubstrate 126; a source region 130 formed on a front side surface of thep body region 128; a gate insulating film 132 disposed on a front sidesurface of the semiconductor substrate 126 between the p body regions128; a gate electrode 138 disposed on the gate insulating film 132; asource electrode 134 connected to the source region 130 and the p bodyregion 128; an n⁺ drain region 124 disposed on a back side surfaceopposite to the surface of the semiconductor substrate 126; and a drainelectrode 136 connected to the n⁺ type drain area 124.

Although the semiconductor chip 110 is composed by including aplanar-gate-type n channel vertical SiC-MISFET in FIG. 27A, thesemiconductor chip 110 may be composed by including an n channelvertical SiC-TMISFET, etc., shown in FIG. 31 mentioned below.

Moreover, a GaN based FET etc. instead of SiC MISFET can also be adoptedto the semiconductor chip 110 (Q) which can be applied to the first orsecond embodiment.

Any one of an SiC based power device or a GaN based power device can beadopted to the semiconductor chip 110 applicable to the first or secondembodiment.

Furthermore, a wide-bandgap type semiconductor of which the bandgapenergy is from 1.1 eV to 8 eV, for example, can be used for thesemiconductor chip 110 applicable to the first or second embodiment.

Similarly, as shown in FIG. 27B, the IGBT as an example of thesemiconductor chip 110A (Q) applicable to the first or second embodimentincludes: a semiconductor substrate 126 composed by including an n− typehigh resistivity layer; a p body region 128 formed on a front surfaceside of the semiconductor substrate 126; an emitter region 130E formedon a front side surface of the p body region 128; a gate insulating film132 disposed on a front side surface of the semiconductor substrate 126between the p body regions 128; a gate electrode 138 disposed on thegate insulating film 132; an emitter electrode 134E connected to theemitter region 130E and the p body region 128; a p⁺ collector region124P disposed on a back side surface opposite to the surface of thesemiconductor substrate 126; and a collector electrode 136C connected tothe p⁺ collector region 124P.

In FIG. 27B, although the semiconductor chip 110A is composed byincluding a planar-gate-type n channel vertical IGBT, the semiconductorchip 110A may be composed by including a trench-gate-type n channelvertical IGBT, etc.

FIG. 28 shows a schematic cross-sectional structure of an SiC MISFETincluding a source pad electrode SP and a gate pad electrode GP, whichis an example of the semiconductor chip 110 applicable to the first orsecond embodiment. The gate pad electrode GP is connected to the gateelectrode 138 disposed on the gate insulating film 132, and the sourcepad electrode SP is connected to the source electrode 134 connected tothe source region 130 and the p body region 128.

Moreover, as shown in FIG. 28, the gate pad electrode GP and the sourcepad electrode SP are disposed on an interlayer insulating film 144 forpassivation which covers the surface of the semiconductor chip 110.Microstructural transistor structure may be formed in the semiconductorsubstrate 126 below the gate pad electrode GP and the source padelectrode SP in the same manner as the center portion shown in FIG. 27Aor 28.

Furthermore, as shown in FIG. 28, the source pad electrode SP may bedisposed to be extended onto the interlayer insulating film 144 forpassivation, also in the transistor structure of the center portion.

FIG. 29 shows a schematic cross-sectional structure of an IGBT includinga source pad electrode SP and a gate pad electrode GP, which is anexample of the semiconductor chip 110A to be applied to the first orsecond embodiment. The gate pad electrode GP is connected to the gateelectrode 138 disposed on the gate insulating film 132, and the emitterpad electrode EP is connected to the emitter electrode 134E connected tothe emitter region 130E and the p body region 128.

Moreover, as shown in FIG. 29, the gate pad electrode GP and the emitterpad electrode EP are disposed on an interlayer insulating film 144 forpassivation which covers the surface of the semiconductor chip 110A.Microstructural IGBT structure may be formed in the semiconductorsubstrate 126 below the gate pad electrode GP and the emitter padelectrode EP in the same manner as the center portion shown in FIG. 27Bor 29.

Furthermore, as shown in FIG. 29, the emitter pad electrode EP may bedisposed to be extended onto the interlayer insulating film 144 forpassivation, also in the IGBT structure of the center portion.

—SiC DIMISFET—

FIG. 30 shows a schematic cross-sectional structure of an SiC DIMISFET,which is an example of a semiconductor chip 110 which can be applied tothe first or second embodiment.

As shown in FIG. 30, the SiC DIMISFET applicable to the first or secondembodiment includes: a semiconductor substrate 126 composed of an n−type high resistivity layer; a p body region 128 formed on a frontsurface side of the semiconductor substrate 126; an n⁺ source region 130formed on a front side surface of the p body region 128; a gateinsulating film 132 disposed on a front side surface of thesemiconductor substrate 126 between the p body regions 128; agateelectrode 138 disposed on the gate insulating film 132; a sourceelectrode 134 connected to the source region 130 and the p body region128; an n′ drain region 124 disposed on a back side surface opposite tothe surface of the semiconductor substrate 126; and a drain electrode136 connected to the n⁺ type drain area 124.

In the semiconductor chip 110 shown in FIG. 30, the p body region 128and the n⁺ source region 130 formed on the front side surface of the pbody region 128 are formed with double ion implantation (DI), and thesource pad electrode SP is connected to the source region 130 and thesource electrode 134 connected to the p body region 128. A gate padelectrode GP (not shown) is connected to the gate electrode 138 disposedon the gate insulating film 132. Moreover, as shown in FIG. 30, thesource pad electrode SP and the gate pad electrode GP (not shown) aredisposed on an interlayer insulating film 144 for passivation configuredto cover the front side surface of the semiconductor chip 110.

As shown in FIG. 30, in the SiC DIMISFET, since a depletion layer asshown with the dashed lines is formed in the semiconductor substrate 126composed of a n− type high resistivity layer inserted into the p bodyregions 128, channel resistance R_(JFET) accompanying the junction typeFET (JFET) effect is formed. Moreover, as shown in FIG. 30, body diodesBD are respectively formed between the p body regions 128 and thesemiconductor substrates 126.

—SiC TMISFET—

FIG. 31 shows a schematic cross-sectional structure of an SiC TMISFET,which is an example of a semiconductor chip 110 which can be applied tothe first or second embodiment.

As shown in FIG. 31, the SiC TMISFET applicable to the first or secondembodiment includes: a semiconductor substrate 126N composed of an n−type high resistivity layer; a p body region 128 formed on a frontsurface side of the semiconductor substrate 126N; an n⁺ source region130 formed on a front side surface of the p body region 128; a trenchgate electrode 138TG passing through the p body region 128, the trenchgate electrode 138TG formed in the trench formed up to the semiconductorsubstrate 126N via the gate insulating layer 132 and the interlayerinsulating films 144U, 144B; a source electrode 134 connected to thesource region 130 and the p body region 128; an n⁺ type drain area 124disposed on a back side surface of the semiconductor substrate 126Nopposite to the front side surface thereof; and a drain electrode 136connected to the n⁺ type drain area 124.

In the semiconductor chip 110 shown in FIG. 31, a trench gate electrode138TG passes through the p body region 128, and the trench gateelectrode 138TG formed in the trench formed up to the semiconductorsubstrate 126N is formed via the gate insulating layer 132 and theinterlayer insulating films 144U, 144B, and the source pad electrode SPis connected to the source region 130 and the source electrode 134connected to the p body region 128. A gate pad electrode GP (not shown)is connected to the gate electrode 138 disposed on the gate insulatingfilm 132. Moreover, as shown in FIG. 31, the source pad electrode SP andthe gate pad electrode GP (not shown) are disposed on an interlayerinsulating film 144U for passivation configured to cover the front sidesurface of the semiconductor chip 110.

In the SiC TMISFET, channel resistance R_(JFET) accompanying thejunction type FET (JFET) effect as the SiC DIMISFET is not formed.Moreover, body diodes BD are respectively formed between the p bodyregions 128 and the semiconductor substrates 126N.

FIG. 32A shows an example of a circuit configuration in which the SiCMISFET is applied as a semiconductor chip, and a snubber capacitor C isconnected between the power terminal PL and the earth terminal (groundterminal) NL, in a schematic circuit configuration of a three-phase ACinverter 140 composed using the semiconductor device according to thefirst or second embodiment. Similarly, FIG. 32B shows an example of acircuit configuration in which the IGBT is applied as a semiconductorchip, and a snubber capacitor C is connected between the power terminalPL and the earth terminal (ground terminal) NL, in a schematic circuitconfiguration of a three-phase AC inverter 140A composed using thesemiconductor device according to the first or second embodiment.

When connecting the semiconductor device according to the first orsecond embodiment to the power source E, large surge voltage Ldi/dt isproduced by an inductance L included in a connection line due to a highswitching speed of the SiC MISFET and IGBT. For example, the surgevoltage Ldi/dt is expressed as follows: di/dt=3×10⁹ (A/s), where acurrent change di=300 A, and a time variation accompanying switchingdi/dt=100 ns. Although a value of the surge voltage Ldi/dt changesdependent on a value of the inductance L, the surge voltage Ldi/dt issuperimposed on the power source V. Such a surge voltage Ldi/dt can beabsorbed by the snubber capacitor C connected between the power terminalPL and the earth terminal (ground terminal) NL.

(Application Examples for Applying Semiconductor Device)

Next, there will now be explained the three-phase AC inverter 140composed using the semiconductor device according to the first or secondembodiment to which the SiC MISFET is applied as the semiconductor chip,with reference to FIG. 33.

As shown in FIG. 33, the three-phase AC inverter 140 includes a gatedrive unit 150, a semiconductor device unit 152 connected to the gatedrive unit 150, and a three-phase AC motor unit 154. U-phase, V-phase,and W-phase inverters are respectively connected to the three-phase ACmotor unit 154 so as to correspond to U phase, V-phase, and W-phase ofthe three-phase AC motor unit 154, in the semiconductor device unit 152.In the embodiments, the gate drive unit 150 is connected to the SiCMISFETs Q1, Q4, SiC MISFETs Q2, Q5, and the SiC MISFETs Q3, Q6.

The semiconductor device unit 152 includes the SiC MISFETs Q1, Q4, andQ2, Q5, and Q3, Q6 having inverter configurations connected between apositive terminal (+) and a negative terminal (−) of the converter 148to which a storage battery (E) 146 is connected. Moreover, flywheeldiodes D1-D6 are respectively connected reversely in parallel betweenthe source and the drain of the SiC MISFETs Q1-Q6.

Next, there will now be explained the three-phase AC inverter 140Acomposed using the first or second semiconductor device 20T according tothe embodiments to which the IGBT is applied as the semiconductor chip,with reference to FIG. 34.

As shown in FIG. 34, the three-phase AC inverter 140A includes a gatedrive unit 150A, a semiconductor device unit 152A connected to the gatedrive unit 150A, and a three-phase AC motor unit 154A. U-phase, V-phase,and W-phase inverters are respectively connected to the three-phase ACmotor unit 154A so as to correspond to U-phase, V-phase, and W-phase ofthe three-phase AC motor unit 154A, in the semiconductor device unit152A. In this case, the gate drive unit 150A is connected to the IGBTsQ1, Q4, IGBTs Q2, Q5, and the IGBTs Q3, Q6.

The semiconductor device unit 152A includes the IGBTs Q1, Q4, and Q2,Q5, and Q3, Q6 having inverter configurations connected between apositive terminal (+) and a negative terminal (−) of the converter 148Ato which a storage battery (E) 146A is connected. Furthermore, flywheeldiodes D1-D6 are respectively connected reversely in parallel betweenthe emitter and the collector of the IGBTs Q1-Q6.

The semiconductor device or the power module according to theembodiments can be formed as any one selected from the group consist of1-in-1 module, 2-in-1 module, 4-in-1 module, 6-in-1 module, and 7-in-1module.

According to the embodiments, there can be provided the semiconductordevice capable of improving the power cycle capability, the powermodule, and the fabrication method of such a semiconductor device.

OTHER EMBODIMENTS

As explained above, the embodiments have been described, as a disclosureincluding associated description and drawings to be construed asillustrative, not restrictive. This disclosure makes clear a variety ofalternative embodiments, working examples, and operational techniquesfor those skilled in the art.

Such being the case, the embodiments cover a variety of embodiments,whether described or not.

INDUSTRIAL APPLICABILITY

The semiconductor device and the power module according to theembodiments can be used for manufacturing techniques of semiconductormodules, e.g. IGBT modules, diode modules, and MOS modules (Si, SiC,GaN), and can be applied to wide applicable fields, e.g. inverters usedfor HEV/EV, inverters and converters used for industrial equipment.

1-20. (canceled)
 21. A semiconductor device comprising: a semiconductorchip on which first and second electrodes are formed on a front surfaceside and a third electrode is formed on a back surface side of thesemiconductor chip, the semiconductor chip comprising a transistor; aninsulating film formed to cover a front surface of the semiconductorchip, the first electrode being disposed on the insulating film, thetransistor being formed below a position where the first electrode isdisposed; a metal layer formed so as to cover at least a part of a frontside surface of the first electrode; and a bonding wire connected on thefront side surface of the first electrode, wherein an area of the firstelectrode is larger than an area of the second electrode.
 22. Thesemiconductor device according to claim 21, wherein the bonding wirecomprising a copper wire.
 23. The semiconductor device according toclaim 21, wherein a plurality of the bonding wires are connected on thefront side surface of the first electrode.
 24. The semiconductor deviceaccording to claim 21, wherein the first electrode includes a concaveportion and a part of the second electrode is inserted into the concaveportion.
 25. The semiconductor device according to claim 21, wherein athickness of the metal layer is within a range from 10 μm to 100 μm. 26.The semiconductor device according to claim 21, wherein thesemiconductor chip is based on an SiC.
 27. The semiconductor deviceaccording to claim 21, wherein the semiconductor chip is disposed on afirst substrate.
 28. The semiconductor device according to claim 21,wherein one end of the bonding wire is bonded onto the metal layer. 29.The semiconductor device according to claim 28, wherein the bonding wirecomprising a copper wire, an aluminum wire, or a clad wire, and the oneend of the bonding wire is bonded thereto by means of an ultrasonicwave.
 30. The semiconductor device according to claim 28, wherein theother end of the bonding wire is connected to a second substrate. 31.The semiconductor device according to claim 21, wherein the metal layeris a fired layer.
 32. The semiconductor device according to claim 31,wherein the fired layer comprises a silver fired layer.
 33. Thesemiconductor device according to claim 31, wherein the fired layercomprises a copper fired layer.
 34. The semiconductor device accordingto claim 21, further comprising: a thin film for coating electrodesurface disposed between the electrode and the metal layer, the thinfilm for coating electrode surface comprising one film selected from thegroup consisting of a gold thin film, a silver thin film and a palladiumthin film.
 35. The semiconductor device according to claim 21, whereinthe semiconductor chip comprises a metal-insulator-semiconductorfield-effect transistor, and the first electrode disposed on thesemiconductor chip comprises a source pad electrode.
 36. Thesemiconductor device according to claim 21, wherein the semiconductorchip comprises a wide-bandgap type semiconductor.
 37. The semiconductordevice according to claim 21, wherein the semiconductor chip is providedwith a ΔTj-power cycle of not less than 100° C.